Hi 500,
You have a "ground loop", one of the most common ills affecting audio and A/V systems, and the power conditioner would be largely (or entirely) a waste of money and may not help. There is no need to "condition" the power for your Adcom amp. It already has a power supply with filters, transformers, etc. and no further filtering is normally required.
First, remove the cheater and use the regular Adcom plug. Now, look at all your connected components (preamp, turntable, video gear, CD player etc.). With the power OFF, reverse the AC plugs one by one of any other components that have a standard 2-prong plug that isn't polarized (one prong is wider than the other, so you can only insert it one way). Each time you reverse a plug, turn on the system with the attached component and your Adcom and see if the hum disappears. In most cases, reversing one or more plugs will eliminate the hum.
If you have a turntable with a separate ground wire, try removing the ground wire from the preamp (if you're using a separate ground). If not, connect the ground wire to the preamp or your Adcom and see if the hum disappears. Likewise, if you are using a powered subwoofer, try reversing the AC plug on the sub and see if the hum disappears on the Adcom. Anything connected to your system with an electrical link is suspect.
If you have any cable feed from a satellite or local cable system remove that, and see if the hum goes away. Often, it does. You may have to insert two cheap balun transformers end to end to "lift" the ground from the cable system, which may be faulty.
Try these fixes before you spend any money on a power conditioner. Keep at it, until you find the source of the hum.
Regards,
